It has been shown that the immersion and treatment of number of Al-based MAX phases with diluted hydrofluoric acid (HF) results in selective removal of Al from the bulk structure and formation of stacked 2D nanosheets of corresponding MX layers that are called MXenes. The aqueous synthesis method of MXenes limits the number of MXenes that can be experimentally synthesized even for removal of Al from some MAX phase structures such as nitride-based MAX phases (i.e., Ti2AlN) or other carbide based MAX phases (i.e. Cr2AlC) where both M and A elements of MXenes are etched. As a result, new methods of preparing MXenes are necessary.
Rechargeable batteries are generally defined as devices which can supply electrical energy and undergo many cycles of charge and discharge to a certain load. In such a system, the electrical energy is stored and produced through transfer of ionic species present in the electrolyte between cathode (positive electrode) and anode (negative electrode). Lithium-ion (Li-ion) batteries that operate based on lithium ions as the active ionic specie have been dominating the market of rechargeable batteries for a long time. However, their safety issues caused by the flammability of the electrolyte and air sensitive materials used in them, high cost of lithium and its limited resources, and the ever-growing demand for energy storage devices has motivated development of other type of rechargeable batteries. Currently, battery systems based on sodium (Na) ions as active ionic species are considered as potential candidate to substitute Li-ion batteries due to lower cost of sodium compared to lithium but they still suffer from similar issues to Li-ion batteries. Other battery systems based on magnesium (Mg) and aluminum (Al) metals are also been investigated but their commercialization is still hindered by lack of proper cathode materials and electrolytes. Particularly, rechargeable aluminum-ion batteries are considered as a promising alternative energy storage devices for Li-ion batteries due to their low cost, abundant resources (aluminum is the most abundant metal in earth crust), low flammability, and three-electron redox reaction leading to high theoretical capacity (theoretical capacity of 2980 mAh/g). As a result, new cathodic materials suitable for using in aluminum batteries are needed.